Magnetic core and method for manufacturing same



Patented Nov. 17, a 1953 UNITED MAGNETIC CORE AND METHOD FORMANUFACTURING SAME Godshalk Berge, Chicago, 111., assignor to AladdinIndustries, Incorporated, Chicago, Ill., a corporation of Illinois NoDrawing.

Application January 3, 1949,

Serial No. 69,043 9 Claims. 01. 252-625) This invention relates tomagnetic cores for use in inductance tuning coils, and it relatesparticularly to the composition and to the method for producing magneticcores which operate efficiently in resonant circuits in the highfrequency television and FM range of about 76.5 to 108 mc.

The characteristics of a magnetic core are often measured by thefrequency range, Q factor and the thermal drift of the core within thefrequency of its intended use. Empirically, it has been shown thatcompositions suitable for use in circuits in the radio frequency orbroadcast range may not be equally suitable for use in circuitsoperating at higher frequencies, such as the ultra high frequency FM andthe television ranges. afiected by the increased frequency is the Qvalue, which may fall to an unusable low value even as a result of aminor increase in frequency.

Optimum conditions are achieved when the magnetic core has the followingcharacteristics, Q in excess of 80, thermal drift which is less than0.01 percent degree centigrade, and range of the desired magnitude inthe frequency band for which it is intended.

It is an object of this invention to provide a magnetic core and amethod for manufacturing the same from commercially available rawmaterials for use in electrical circuits, especially in the televisionand FM range.

Another object is to provide a magnetic core that has thecharacteristics of high Q, low thermal drift and satisfactory rangewithin the high frequency bands of 76 to 108 mc. I

A further object is to provide a new method for producing magnetic coresfor use in circuits, operating in these very high frequency ranges,which method includes the combination of commercially available rawmaterials to produce stable magnetic compounds and the combination ofthese compounds in various proportions, with and without modifyingsubstances to form the final product.

I have found that the characteristics of a magnetic core may not dependentirely upon the raw materials and the elements of which it is formed,but important also is the arrangement which those elements assume in thefinal product. I have found that certain metal oxides when compoundedtogether develop magnetic properties, and in their compounded formcontribute materially to the desirable characteristics secured in coresforming the subject matter of this invention. I have found further thatthese oxides should be formedto stable compounds The characteristic mostoften and that the amounts and types of additives should be closelycontrolled; otherwise, the composition of the compounds will be alteredeither by chemical reaction or by displacement with more activeelements, whereupon the effect of the materials present is greatlyminimized.

For example, a core formed by reaction in combination of iron oxide(FezOa), cobalt oxide (C0203), nickel oxide (NiaOs), zinc oxide (ZnO),vanadium oxide (V205), and magnesium zirconate (MgZrOz) does not havecharacteristics comparable to a magnetic core formed from the samematerials having a molecular arrangement of the type secured by myinvention. When practicing my invention with the above materials, thefinal product is a magnetic core having a frequency range of 108 to 76.5mc., a Q of which remains practically constant over the entire range,and an exceptionally low thermal drift of about 0.004 percent degreecentigrade.

An important feature of my invention resides in the formation of stablesalts of the cobalt or nickel components by the separate reaction of thecobalt or nickel oxides in sufiicient amount to form whatis believed tobe the corresponding cobalt or nickel ferrites. The amount of ma terialemployed for carrying out the invention may most easily be designated interms of molecular equivalents since two molecular weights of iron oxideappear to thermally react with one molecular weight of the cobalt ornickel oxides in the formation of the corresponding salts according tothe following formulae:

Strict adherence to amounts determined on the basis of molecularequivalents is not essential because acceptable results can be securedby variation of one or the other of the oxides by about 10 per cent fromthe theoretically calculated amount.

In specific application, the oxide of iron in finely divided form ismixed with the oxide of cobalt or the oxide of nickel in finely dividedform and the mass is fired for about two hours at 2200 F. The time offiring might be varied according to the temperature employed and themass to be reacted. For example, proper firing may require 3 to 4 hoursat 2000 F., while 1 hour or less may suflice when reaction is carriedout at a temperature of 2500 F. The reaction product, when cooled toroom temperature, is a hard friable mass having magnetic properties,

and for further processing into magnetic cores, it is reduced to finelydivided form.

Although magnetic cores might be formed of the finely divided reactionproducts of nickel oxide with iron oxide, or of cobalt oxide with ironoxide, I prefer to combine the two reaction products in substantiallyequal proportions or with one in excess of the other up to about 25percent. Core formation is effected by a molding operation followed by aheat treatment to a temperature of about 1800 to 2350 F. for about 1 ormore hours. Best results are secured when the heat treated cores aregradually cooled to room temperature at a rate, for example, of about100 F. per hour. My invention is not limited to the above describedconditions since the time of heat treatment may vary according to thetemperature used and the rate of cooling is influenced by the mass ofmaterial involved.

Temporary cohesive strength is imparted to the molded product prior toheat treatment by the admixture of a small amount of resinous binderwhich may include the reaction products of phenol-aldehydes,urea-aldehydes, vinylpolymers and copolymers, poiyacrylates,polystyrene, and the like. Up to percent bindermay be used, however, 2to 3 percent ordinarily is sufficient. The described binders are heatsensitive and are subject to thermal decomposition as the temperature ofheat treatment exceeds 500 F., whereupon the greater portion of thebonding action secured thereby is lost and reliance is had upon thedevelopment of a bond by one or more of the metallic substances makingup the core composition, which bond is usually developed at highertemperatures.

Although magnetic cores can be produced solely from the reactionproducts of the oxides of cobalt and nickel with iron oxides, zinc oxidemay be added to extend the frequency range which is obtained by means ofthe cores, especially when used in amounts corresponding to less thanpercent by weight of the final prodnot.

To prevent unstabilization of the core ingredients formed by reaction ofcobalt oxides and nickel oxides with iron oxide, such as by displacementof either the nickel or cobalt atom by the more basic zinc atom,sufiicient additional iron oxide should be incorporated in the mix toneutralize the zinc oxide. The addition of zinc oxide and correspondingamounts of iron oxide to the described reaction products might be madeduring the core forming process, but in many instances, best results aresecured when the added substances are first reacted at firingtemperature corresponding to those previously described to efiect theformation of a neutral salt, believed to be zinc ferrite. Zinc oxide andiron oxide combine in substantially equi-molecular proportions and,therefore, it is expedient to designate the amounts that may be added insuch terms, it being understood that variations of about 10 percent fromtheoretically calculated amounts are permissible. Although it isundesirable to disturb the neutral salts of cobalt and nickel, a smallamount of displacement by zinc may be unavoidable under the conditionsemployed in the heat treatment.

Further improvement in the properties of a manufactured magnetic core issecured by the addition, previous to molding, of a small amount ofvanadium oxide to the ingredients from which the core is manufactured.Vanadium oxide functions chiefly to expand the frequency range obtainedwith the core and for this purpose, amounts up to 5 percent by weight ofthe core composition have been successfully used. The improvementsecured by further additions does not warrant the added cost of vanadiumoxide and, therefore, I prefer to limit my use to less than 10 percent,

During heat treatment, it appears that a stable salt is formed byreaction of vanadium oxide with iron oxide, the major reaction product,possibly being ferro-vanadanite. To bring about this reaction,suflicient additional iron oxide is added, or else is allowed to remainunneutralized in the previously described reaction products.

is. very important feature of this invention resides in the use ofmagnesium zirconate in the core compositions previously described.Importance is directed to the addition of magnesium zirconate because ithas the novel and very desirable characteristic of substantiallyreducing the thermal drift while supporting the Q values of thecompounded materials. Magnesium zirconate is effective when used inamounts up to 12 percent by weight of the composition, and best use ismade when used in amounts ranging from 4 to 8 percent. The same effecton thermal drift cannot be secured by the addition of other commonlyused materials, such as zirconium oxide, magnesium titanite, strontiumtitanite, or calcium stannite. When used in designated amounts,magnesium titanite can be substituted in part with about 25 percent byweight lead titanite.

It will be manifest that the materials set forth may be formulatedtogether within the weight limitations prescribed to secure magneticcores having excellent characteristics with respect to range, Q, andthermal drift, in television or FM circuits. It will be understood thatthese same compositions might also be used in lower frequency circuitssuch as radio frequencies and the like. The additive materials may becompounded with the separate thermal reaction products formed of cobaltand nickel and zinc oxides with iron oxide, and with zinc oxide, unlesspreviously separately reacted with iron oxide, and then molded to coreformation followed by'heat treatment under the conditions previouslydescribed. With these materials in the desired arrangement, inequalitiesin density which normally follow molding under high pressure, arecompensated by unequal shrinkage during heat treatment to the extentthat a magnetic core is secured having substantially equal permeabilitythroughout.

The following examples given by way of illustration, but not by way oflimitation, describe the manufacture of magnetic cores in accordancewith this invention.

EXAIVIPLEI Materials 56 percent iron oxide (FeaOa) 10 percent cobaltoxide (C0203) 8 percent nickel oxide (NizOa) 13 percent zinc oxide (ZnO)5 percent vanadium oxide (V205) 8 percent magnesium zirconate (MgZrOa)Cobalt oxide and nickel oxide are separatelywith the other ingredients,and compounded with about 2 to percent "A" stage phenol formaldehyderesin dissolved in alcohol medium. The composite mass is molded to coreshape under about 2000 pounds per square inch pressure and then heattreated for about two hours at 2000 F. The heat treated core is cooledto room temperature by decrements of 100 per hour. The product has thefollowing characteristics:

Range 108-765 Thermal drift 0.004 percent per C.

' EXAMPLE 2 The amount of material employed is the same as that inExample 1 above. The cobalt oxide, nickel oxide and zinc oxide areseparately mixed with the required molecular equivalents of iron oxideand fired at a temperature of about 2200 F. for about 1 /2 hours. Whencooled to room temperature, the reaction products are subdivided topowdery form and mixed with the vanadium oxide, magnesium zirconate andthe remaining iron oxide. To this mixture about 2.5 percent byweight-phenol formaldehyde resinous binder are added and then it ismolded to core formation. The molded product is subjected to heattreatment in the manner previously described in Example l, except thatthe heat treatment is carried out at 2000 F. for 1 hours. Thecharacteristics of the resulting magnetic core correspond substantiallywith those secured by the use of the same elements in Example 1.

EXAMPLE 3 Materials 58 percent iron oxide 12 percent cobalt oxide '1percent nickel oxide 12 percent zinc oxide 3 percent vanadium oxide 8percent magnesium zirconate Range 78-108 Q 80 Thermal drift 0.004percent per C.

It will be manifest from the description that I have found a new andimproved ystem relating to the reaction of materials to form salts andcomplexes which when compounded into cores with or without additiveshave material effect upon the characteristics of the magnetic core atrelatively high frequencies. These same effects are not secured when thematerial are not first reacted in the described manner to provide suchcompounds and complexes which it is desirable to have in unmodified formin the final product. To the best of my knowledge, no one before hasdeemed it desirable to form the magnetic core with products formed bythe separate thermal reaction of nickel oxide and of cobalt oxide withiron oxide present in sufficient amounts to form a stable salt. havingmagnetic properties. Although the addition of zinc oxide to variouselements has previously been considered to extend the range of the core,no one before has found that it is important to control the addition ofzinc oxide to minimize its effect upon the described reaction products.Importance is directed to the addition of magnesium zirconate which iseffective drastically to reduce the thermal drift of these and othercore compositions by amounts not heretofore contemplated.

It will be understood that the magnetic cores produced by the materialsdescribed in thi invention find best use in the high frequency rangesbut may also be advantageously used at lower frequencies. It will befurther understood that numerous changes may be made in the amounts ofmaterials, and the order of incorporation and the conditions under whichthey are reacted without departing from the spirit of the invention,especially as defined in the following claims.

I claim as my invention:

1. The method of manufacturing magnetic cores, comprising the steps ofseparately reacting NizOs, C0203 and ZnO with F6203 in the ratio of oneequivalent weight of the nickel and cobalt oxides to about twoequivalent weight of iron oxide and one molecular weight of zinc oxideto one molecular equivalent iron oxide at a temperature within the rangeof 2000-2500" F. for from 1-4 hours, compounding the reaction productsin finely divided form with vanadium oxide and magnesium zirconate and abinder in amounts ranging up to 8 percent of the mix, molding the mix tomold shape, heat treating the molded mass at a temperature within therange of 1800- 2200 F. for /2-2 hours, and then slowly cooling the heattreated mass to room conditions, the material being incorporated inamounts ranging from 8-12 parts cobalt oxide, 6-12 parts nickel oxide,5-15 parts zinc oxide, 1-10 parts vanadium oxide, 4-12 parts magnesiumzirconate, and 40-65 parts iron oxide.

2. In the method of manufacturing magnetic cores, the steps ofseparately thermally reacting NizOs, C0203, zinc oxide and vanadiumoxide with about two molecular equivalents of Fezoa per molecularequivalent of nickel oxide and cobalt oxide and one molecular equivalentof iron oxide per molecule of zinc oxide and vanadium oxide respectivelyat a temperature within the range of 2000-2500 F. for 1-4 hours, mixingthe reaction products in finely divided form with the amount of thereaction product of zinc oxide and vanadium oxide being based upon asmall amount up to about 15 percent zinc oxide and a small amount up toabout 10 percent vanadium oxide based upon the mixture, molding thereaction product to core shape with less than 10 percent by weight of atemporary organic binder, and then heating the molded mass to atemperature between 1800-2350 F. for 1-2 hours.

3. In the method of manufacturing magnetic cores, the steps ofseparately thermally reacting NizOa, C0203, zinc oxide and vanadiumoxide with about two molecular equivalents of F820: per molecularequivalent of cobalt and nickel oxide and one molecular equivalent ofiron oxide per molecule of ,zinc oxide and vanadium oxide respectivelyat a temperature within the range of 2000-2500 F. for l-4 hours, mixingthe reaction products in proportions ranging from equal parts byweightto an excess of 25 percent 'by weight of the reaction product ofnickel and cobalt oxide with iron oxide and a small amount up to about15 percent by weight of zinc oxide as its reaction product and a smallamount up to about 10 percent by weight of vanadium oxide as itsreaction product with the reaction products in finely divided form andcombined with up to 10 percent by weight of a temporary organic binderand 4-12 percent by weight of magnesium zirconate,

molding the mass to core shape and then heating the molded mass to atemperature between 1800-2350 F. for at least /2 hour.

4. In the method of manufacturing magnetic cores, the steps ofseparately thermally reacting NizOa and C020; in the ratio of equalparts by weight to an excess of 25 percent by weight of one over theother with about two molecular equivalents of iron oxide at atemperature within the range of 2000-2500" F. for 1-4 hours, mixing thereaction products in finely divided form with a small amount up to aboutpercent by weight of a temporary organic 'binder, a small amount up toabout 12 percent by weight of magnesium zirconate, a small amount up toabout 15 percent by weight zinc oxide and a small amount up to about 10percent by weight vanadium oxide with sufllcient iron oxide to reactwith the zinc and vanadium oxides to form the corresponding ferrite,molding the mass to core shape and then heating the molded mass to atemperature between 1800-2350 F. for at least /2 hour.

5. The method of manufacturing magnetic cores, comprising the steps ofmixing nickel ferrite and cobalt ferrite as major ingredients in theratio of equal parts by weight to an excess of 25 percent by weight ofone over the other with zinc ferrite in amounts less than 15 percent byweight calculated on the basis of zinc oxide, the thermal reactionproduct of vanadium and iron oxide present in amounts less than 10percent by weight calculated on the basis of vanadium oxide, and lessthan 10 percent by weight of a temporary organic binder, molding themixture to core shape and then heating the molded mass to a temperaturewithin the range of 1800-2350 F. for about -2 hours.

6. The method of manufacturing magnetic cores, comprising the steps ofmixing nickel ferrite and cobalt ferrite as major ingredients present inthe ratio of equal parts by weight to an excess or 25 percent by weightor one over the other with zinc ferrite in amounts ranging up to 15percent by weight calculated on the basis of zinc oxide, the thermalreaction product of vanadium and iron oxide in amounts ranging up to 10percent by weight calculated on the basis of vanadium oxide, 4-12percent by weight of magnesium zirconate and up to 10 percent by weightof a temporary organic binder, molding the mass to core shape and thenheating the molded mass to a temperature within the range of 1800-2350F. for about -2 hours.

7. A magnetic core formed by the method of claim 5.

8. A magnetic core formed by the method of claim 6.

9. A magnetic core as claimed in claim 8 in which magnesium zirconatemay be substituted in amounts up to 25 percent by weight thereof by leadtitanite.

GODSHALK BERGE.

References cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,997,193 Kato et al. Apr. 9, 1935 FOREIGN PATENTS NumberCountry Date 226,347 Germany Sept. 29, 1910 OTHER REFERENCES Kawai:Journal of the Society of Chemical Industry, Japan, vol. 37, No. 4(1934), page 1743.

"Non-Metallic Magnetic Material for High F'requencies, Snoek-PhillipsTechnical Review, vol. 8, No. 12, December 1946; pages 353-360.

1. THE METHOD OF MANUFACTURING MAGNETIC CORES, COMPRISING THE STEPS OFSEPARATELY REACTING NI2O3, CO2O3 AND ZNO WITH FE2O3 IN THE RATIO OF ONEEQUIVALENT WEIGHT OF THE NICKEL AND COBALT OXIDES TO ABOUT TWOEQUIVALENT WEIGHTS OF IRON OXIDE AND ONE MOLECULAR WEIGHT OF ZINC OXIDETO ONE MOLECULAR EQUIVALENT IRON OXIDE AT A TEMPERATURE WITHIN THE RANGEOF 2000-2500* F. FOR FROM 1-4 HOURS, COMPOUNDING THE REACTION PRODUCTSIN FINELY DIVIDED FORM WITH VANADIUM OXIDE AND MAGNESIUM ZIRCONATE AND ABINDER IN AMOUNTS RANGING UP TO 8 PERCENT OF THE MIX, MOLDING THE MIX TOMOLD SHAPE, HEAT TREATING THE MOLDED MASS AT A TEMPERATURE WITHIN THERANGE OF 18002200* F. FOR 1/2-2 HOURS, AND THEN SLOWLY COOLING THE HEATTREATED MASS TO ROOM CONDITIONS, THE MATERIALS BEING INCORPORATED INAMOUNTS RANGING FROM 8-12 PARTS COBALT OXIDE, 6-12 PARTS NICKEL OXIDE,5-15 PARTS ZINC OXIDE, 1-10 PARTS VANADIUM OXIDE, 4-12 PARTS MAGNESIUMZIRCONATE, AND 40-65 PARTS IRON OXIDE.